Method and device for inspection of liquid articles

ABSTRACT

Disclosed are a method and a device for security-inspection of liquid articles with dual-energy CT imaging. The method comprises the steps of obtaining one or more CT images including physical attributes of liquid article to be inspected by CT scanning and a dual-energy reconstruction method; acquiring the physical attributes of each liquid article from the CT image; and determining whether there are drugs concealed in the inspected liquid article based on the difference between the acquired physical attributes and reference physical attributes of the inspected liquid article. The CT scanning can be implemented by a normal CT scanning technique, or a spiral CT scanning technique. In the normal CT scanning technique, the scan position can be preset, or set by the operator with a DR image, or set by automatic analysis of the DR image.

FIELD OF THE INVENTION

The present invention is related to the field of radiation inspectiontechnique, and more particularly to a method and device for quicksecurity-inspection of liquid articles with dual-energy CT.

BACKGROUND OF THE INVENTION

Since 9•11 in U.S., security-inspection of aviation is becoming more andmore emphasized. Besides conventional security-inspection of packages,security-inspection of the liquid articles carried by passengers isadded. Accordingly, it is in dire need of means and methods for quicksecurity-inspection of the liquid articles.

Nowadays, there are four types of methods used in security-inspection ofliquid articles, including chemical method, electromagnetic method,neutron detection method and radiation detection method as follows:

1) The chemical method can be subdivided into odor identificationmethod, ion scanning explosive detection method and substance analysismethod. The odor identification in practical applications often fails toimplement detection because of sealed and packaged conditions of liquidarticles. The ion scanning explosive detection method is known for itshigh sensitivity, but with high false alarm rate, it suffers from theaffection of background environment. The substance analysis is of highprecision and high accuracy, but this method needs a certain period oftime to analyze the sample, which cannot meet the demands of on-sitequick detection.

2) The electromagnetic method works in an active measurement manner. Itdistinguishes liquid articles from each other according to theirdielectric constants in an electromagnetic field. The electromagneticmethod is easily subjected to severe affection of metal packages orother thick material packages. As a result, the use of electromagneticmethod is limited in case of complex package materials.

3) The use of the neutron detection method will leave residual radiationremaining in the detected liquid due to the effect of “neutronactivation”. Furthermore, the radiation shielding is complicate due toneutrons' strong penetrability, and the apparatus has to take a largearea, so the method is not suitable for application in thesecurity-inspection systems of civil aviation.

4) Currently, most of the security-inspection apparatuses for civilaviation are radiation apparatuses. In these apparatuses, the 2D X-rayimaging technology and three-dimensional CT technology are mostlyadopted. These technologies, which can obtain structure information ofarticles, fail to determine whether there are drugs concealed in theliquid articles. The reason is that the overall structure (for example,the number of layers) of the liquid articles will not change a lot withdrugs being concealed therein, only the components will change.

To sum up, for the quick detection of the liquid articles, the chemicalmethod, the electromagnetic method and the neutron detection method arenot suitable. By using the 2D X-ray imaging technology and thethree-dimensional CT technology, images including the structureinformation of the article are acquired, but these images cannot work assufficient evidence for whether there are drugs concealed in the liquidarticles.

SUMMARY OF THE INVENTION

In order to overcome the disadvantages in the existing technologies, anobject of the invention is to provide a method as well as a device forsecurity-inspection of a liquid article using radiations, which canconduct a quick detection and get quantitative information of the liquidarticle to be inspected, without destroying the outer packing.

In the first aspect of the invention, the invention provides a methodfor security-inspection of a liquid article with dual-energy CT,comprising the steps of: acquiring dual-energy projection data bydual-energy CT scanning on the liquid article to be inspected;performing CT reconstruction on the projection data to obtain a CT imagewhich indicates physical attributes of the inspected liquid article;extracting the physical attributes of the inspected liquid article basedon the CT image; and determining whether the inspected liquid article issuspicious according to the physical attributes and reference physicalattributes of the inspected liquid article.

According to an embodiment of the invention, the physical attributesinclude the density and atomic number of the liquid article.

According to an embodiment of the invention, the dual-energy CT scanningworks in a plane CT scanning manner.

According to an embodiment of the invention, the dual-energy CT scanningworks in a normal spiral CT scanning manner.

According to an embodiment of the invention, the dual-energy CT scanningworks in a high pitch spiral CT scanning manner.

According to an embodiment of the invention, a set of scan positions arepreset prior to the plane CT scanning.

According to an embodiment of the invention, a DR scanning is performedto get a transmission image of the inspected article and the CT scanposition is determined based on the transmission image, prior to theplane CT scanning.

According to an embodiment of the invention, after the transmissionimage has been gotten, the operator specifies at least one row of thetransmission image via an input device as the CT scan position.

According to an embodiment of the invention, after the transmissionimage has been gotten, at least one row of the transmission image isautomatically specified by the image processing technique as the CT scanposition.

According to an embodiment of the invention, the step of getting thetransmission image comprises emitting high-energy radiation beams andlow-energy radiation beams which transmit the inspected article to forma high-energy transmission image and a low-energy transmission image;integrating the high-energy transmission image and the low-energytransmission image to form the transmission image.

According to an embodiment of the invention, the step of forming thetransmission image comprises emitting high-energy radiation beams andlow-energy radiation beams which transmit the inspected article to forma high-energy transmission image and a low-energy transmission image;selecting either the high-energy transmission image or the low-energytransmission image as the transmission image.

According to an embodiment of the invention, the step of performing CTreconstruction on the projection data to obtain a CT image whichindicates physical attributes of the inspected liquid article comprisesthe steps of: generating projection data of two basis materialcoefficients based on the high-energy and low-energy projection data;performing reconstruction on the projection data of the two basismaterial coefficients to obtain a CT image which indicates the two basismaterial coefficients corresponding to the inspected liquid article; andgenerating a CT image to indicating physical attributes of the inspectedliquid article based on the CT image indicating the basis materialcoefficients.

According to an embodiment of the invention, the step of extracting thephysical attributes of the inspected liquid article based on the CTimage comprises the steps of extracting pixels corresponding to theliquid article from the CT image; calculating the average density andatomic number of the pixels corresponding to the liquid article as thedensity and atomic number of the inspected liquid article.

According to an embodiment of the invention, the step of determiningwhether the inspected liquid article is suspicious according to thephysical attributes and reference physical attributes of the inspectedliquid article comprises the steps of calculating the difference betweenthe density and atomic number and reference density and atomic number;and determining there are drugs concealed in the inspected liquidarticle if the difference is larger than a predetermined threshold.

According to an embodiment of the invention, after dual-energy CTscanning at each of the positions, the CT images of the inspected liquidarticle are rotated to be aligned with the image formed after the firstdual-energy CT scanning.

According to an embodiment of the invention, after dual-energy CTscanning at each of the positions, the inspected liquid article isrotated to the position before scanning.

According to an embodiment of the invention, several liquid articles aredisposed in a barrel which is divided into multiple subspaces.

According to an embodiment of the invention, the method furthercomprises steps of automatically detecting the presence of the barrelwith a predefined pattern; determining a certain mark in the CT image inthe case of the presence of the barrel; and rotating the barrel to apredefined position based on the certain mark.

According to an embodiment of the invention, the method furthercomprises the step of displaying determining result of the inspectedliquid article on a display screen.

According to an embodiment of the invention, the method furthercomprises the step of printing determining result of respective liquidarticles.

According to an embodiment of the invention, the method furthercomprises the step of colorizing the CT images of respective liquidarticles.

In another aspect of the invention, the invention provides a device forsecurity-inspection of a liquid article with dual-energy CT, comprising:a radiation source for emitting radiation beams; detection andcollection means for detecting and collecting radiation beamstransmitting at least one liquid article to be inspected; a controllerfor controlling the radiation source and the detection and collectionmeans to perform dual-energy CT scanning on the inspected liquid articleso as to obtain projection data; means for performing reconstruction onthe projection data to obtain a CT image which indicates at least onephysical attribute of the inspected liquid article; and means fordetermining whether the inspected liquid article is suspicious based onthe physical attribute and reference physical attributes of theinspected liquid article.

According to an embodiment of the invention, the dual-energy CT scanningis performed on a predetermined position.

According to an embodiment of the invention, the detection andcollection means detects and collects radiation beams transmitting theat least one liquid article to be inspected so as to form a transmissionimage; wherein the device further comprises means for specifying atleast one row of the transmission image; and the dual-energy CT scanningis performed on the specified row.

According to an embodiment of the invention, the physical attributesincludes at least the density and atomic number of the inspected liquidarticle.

According to an embodiment of the invention, the radiation source emitshigh-energy radiation beams and low-energy radiation beams whichtransmit the inspected article to form a high-energy transmission imageand a low-energy transmission image; and the device further comprisesmeans for integrating the high-energy transmission image and thelow-energy transmission image to form the transmission image.

According to an embodiment of the invention, the radiation source emitshigh-energy radiation beams and low-energy radiation beams whichtransmit the inspected article to form a high-energy transmission imageand a low-energy transmission image; and the device further comprisesmeans for selecting either the high-energy transmission image or thelow-energy transmission image as the transmission image.

According to an embodiment of the invention, the means for specifying atleast one row of the transmission image comprises means for selecting atleast one row by the operator from the transmission image via an inputdevice.

According to an embodiment of the invention, the means for specifying atleast one row of the transmission image comprises means for detectingliquid layers in the transmission image by analyzing pixels of thetransmission image; and means for specifying central rows of respectivelayers as the rows to be performed dual-energy CT scanning.

According to an embodiment of the invention, the means for performingreconstruction on the projection data to obtain a CT image whichindicates physical attributes of the inspected liquid article comprisesmeans for integrating a density image identified by the density of theinspected liquid article and an atomic number image identified by theatomic number of the inspected liquid article to form a CT image; andmeans for extracting pixels corresponding to the liquid article from theCT image; and means for calculating the average density and atomicnumber of the pixels corresponding to the liquid article as the densityand atomic number of the inspected liquid article.

According to an embodiment of the invention, the means of determiningwhether the inspected liquid article is suspicious according to thephysical attributes and reference physical attributes of the inspectedliquid article comprises means of calculating the difference between thedensity and atomic number and reference density and atomic number; andmeans of determining there are drugs concealed in the inspected liquidarticle if the difference is larger than a predetermined threshold.

According to an embodiment of the invention, the device furthercomprises means for, after dual-energy CT scanning at each of the rows,rotating the CT images of the inspected liquid article to be alignedwith, the image formed after the first dual-energy CT scanning.

According to an embodiment of the invention, the device furthercomprises means for, after dual-energy CT scanning at each of the rows,rotating the inspected liquid article to the position before scanning.

According to an embodiment of the invention, the device furthercomprises a barrel which is divided into multiple subspaces fordisposing a plurality of liquid articles respectively.

According to an embodiment of the invention, the device furthercomprises means for automatically detecting the presence of the barrelwith a predefined pattern; means for determining a certain mark in theCT image in the case of the presence of the barrel; and means forrotating the barrel to a predefined position based on the certain mark.

According to an embodiment of the invention, the device furthercomprises display means for displaying determining result of theinspected liquid article.

According to an embodiment of the invention, the device furthercomprises means for printing determining result of respective liquidarticles.

According to an embodiment of the invention, the device furthercomprises means for colorizing the CT images of respective liquidarticles.

According to an embodiment of the invention, the device furthercomprises a carrier mechanism to carry the liquid articles to beinspected, wherein the surface of the carrier mechanism on which theinspected liquid articles is carried is divided into a plurality ofregions the operator can identify.

In yet another aspect of the invention, the invention provides a devicefor security-inspection of a liquid article with dual-energy CT,comprising a radiation source for emitting radiation beams; detectionand collection means for detecting and collecting radiation beamstransmitting at least one liquid article to be inspected; a controllerfor controlling the radiation source and the detection and collectionmeans to perform spiral CT scanning on the inspected liquid article soas to obtain a set of spiral CT images each of which indicates at leastone physical attribute of the inspected liquid article; means foranalyzing the set of spiral CT images to acquire a spiral CT image partof the liquid article; and means for determining whether the inspectedliquid article is suspicious based on the physical attribute andreference physical attribute of the inspected liquid article.

According to an embodiment of the invention, the physical attributesincludes at least the density and atomic number of the inspected liquidarticle.

With the method and device according to the invention, the transmissionimage is used as a guide for the dual-energy scanning, and thus thedetection speed can be improved without lowing detection accuracy.Furthermore, it can be determined whether the liquid article has aninterlayer by means of the transmission image.

Moreover, it can be determined whether there are drugs (for example,cocaine etc.) concealed in liquid articles (for example, alcohol) bycomparing the measured density and atomic number with reference densityand atomic number.

In addition, inspection operation is facilitated because the operatorcan specify any position to perform the dual-energy CT scanning.

Further, a divided barrel is used when a plurality of articles is to beinspected, and so it can be easily determined which one of the liquidarticles is suspicious.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention can be more apparent fromthe following detailed descriptions with reference to the accompanyingdrawings in which,

FIG. 1 is a schematic diagram of an inspection device according to anembodiment of the present invention;

FIG. 2 shows a block diagram of the computer data processor 60 in theinspection device of FIG. 1;

FIG. 3 shows a block diagram of the controller according to a firstembodiment of the present invention;

FIG. 4 shows a structure used for storing identification information andattribution information of various liquid articles in a database;

FIG. 5 is a diagram showing the relationship between a DR imaging and aCT imaging;

FIG. 6 shows an example of the result of the DR imaging;

FIG. 7 shows another example of the result of the DR imaging;

FIG. 8 shows an outline flowchart of the liquid article inspectionmethod according to the first embodiment of the invention;

FIG. 9 shows a flowchart of the process of a DR imaging;

FIG. 10 shows an arrangement of the DR image data collected by thedetection and collection device 30 during the process of the DR imaging;

FIG. 11 shows a flowchart of a process of determining a CT scan positionby processing DR image;

FIG. 12 shows a process for CT imaging;

FIG. 13 shows an arrangement of the CT projection data during theprocess of the CT imaging;

FIG. 14 shows a process for measuring the attributes of the liquid;

FIG. 15 shows a process for expanding the database;

FIG. 16A and FIG. 16B show diagrams of CT images reconstructed in thecase that there are several liquid articles to be inspected according toa second embodiment of the present invention;

FIG. 17A to FIG. 17K show a process how to rotate the CT reconstructionimages and/or the carrier mechanism to be aligned with the positionbefore CT scanning;

FIG. 18 shows a flowchart for performing inspection operation in thecase of there are several articles to be inspected;

FIG. 19 shows a top view of the carrier mechanism according to a secondembodiment of the present invention;

FIG. 20 shows a side view of a divided barrel according to an embodimentof the invention;

FIG. 21 shows a top view of a divided barrel;

FIG. 22 shows a bottom view of a divided barrel;

FIG. 23 shows a process how to automatically detect the divided barreland the mark during an inspection operation;

FIG. 24A to FIG. 24D shows a diagram of a process of rotating the barrelduring the inspection operation;

FIG. 25 shows a flowchart of the inspection operation according to athird embodiment of the invention;

FIG. 26A shows a change curve of the density after drugs are concealedin the liquid;

FIG. 26B shows a change curve of the atomic number after drugs areconcealed in the liquid;

FIG. 26C shows a change curve of the characteristic density after drugsare concealed in the liquid;

FIG. 27 illustrates a flowchart of the inspection operation according toa fourth embodiment of the invention;

FIG. 28 is a diagram for explaining the spiral CT scanning process ofthe liquid article;

FIG. 29A to FIG. 29M are diagrams illustrating the images obtained byperforming spiral CT scanning on the liquid article.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the invention will now be described morefully hereinafter with reference to the accompanying drawings. In thedrawings the same reference numerals are used for denoting the same orsimilar components that are shown in different figures. For clarity, thedetailed description of the known function and structure incorporatedherein will be omitted, which would otherwise weaken the subject of theinvention.

First Embodiment

FIG. 1 is a schematic diagram of the structure of an inspection deviceaccording to an embodiment of the invention.

As shown in FIG. 1, the inspection device according to the inventioncomprises a radiation source 10 for emitting dual-energy X-rays forinspection, e.g. a X-ray machine; a carrier mechanism 40 which carriesthe liquid article 20 to be inspected and can rotate around axis Zthereof and can ascend or descend to take the liquid article 20 into theinspection area, thereby the radiations emitted by the radiation source10 can transmit through the inspected liquid article 20; a detection andcollection means 30 being an integrated module of a detector and a datacollector, which is used to detect the dual-energy radiationstransmitted through the liquid article 20 to acquire analog signals, andconvert the analog signals into digital signals, and hence output thescanning data of the liquid article 20 with respect to the high energyX-rays and low energy X-rays; a controller 50 which controls eachcomponent of whole system so that they operate synchronously; and acomputer data processor 60 for processing the data collected by the datacollector and outputting inspection results.

As shown in FIG. 1, the radiation source 10 is placed at one side of thecarrier mechanism 40 carrying the liquid article 20 to be inspected,while the detection and collection means 30 is placed at the other sideof the carrier mechanism 40. The detection and collection means 30comprises a detector and a data collector for acquiring the DR data andthe multi-angle projection data of the liquid article 20. The datacollector has a signal amplifying and shaping circuit, which operatesunder (current) integration mode or pulses (counting) mode. Thedetection and collection means 30 has its data output cable connectedwith the computer data processor 60 to store the collected data into thecomputer data processor 60 according to trigger instructions.

Besides, the inspection device also comprises a cylindrical articlepassage 20 made of metals and having openings at lower portions of sidewall to allow the liquid article can be irradiated by radiations andshield some of the radiations that do not irradiate the liquid articles.The inspected liquid article 20 is placed in the article passage.

FIG. 2 shows a block diagram of the computer data processor 60 ofFIG. 1. As shown in FIG. 2, the data collected by the data collector arestored in the memory 61 through an interface unit 68 and a bus 64. Theconfiguration data and programs of the to computer data processor arestored in the ROM (Read Only Memory) 62. The RAM (Random Access Memory)63 is used for temporarily storing various data during the operatingprocedure of the processor 66. Besides, computer programs for dataprocessing and a pre-compiled database are also stored in the memory 61,the database storing relevant information of various known liquidarticles, such as names, kinds and physical attributes for comparingwith the attributes such as density and atomic number of the inspectedliquid article calculated by the processor 66. The internal bus 64connects the memory 61, the ROM 62, the RAM 63, the input device 65, theprocessor 66, the display device 67 and the interface unit 68 together.

After the user inputs operation commands through the input device 65such as keyboards and mouse, the instruction code of the computerprograms will instruct the processor 66 to perform a predetermined dataprocessing algorithm. After the processing results are obtained, theywill be displayed on the display device 67 such as a LCD, or redirectedin the form of a hard copy such as printing.

FIG. 3 shows a block diagram of the controller according to a firstembodiment of the invention. As shown in FIG. 3, the controller 50comprises a control unit 51 for controlling the radiation source 10, thecarrier mechanism 40 and the detection and collection means 30 based oninstructions from the computer 60; a trigger signal generation unit 52for generating trigger commands for triggering the radiation source 10,the detection and collection means 30 and the carrier mechanism 40 tooperate under the control of the control unit 51; a first driving motor55 for driving the carrier mechanism 40 to ascend or descend accordingto the trigger command generated by the trigger signal generation unit52 under the control of the control unit 51; a height informationacquirement unit 53 for feeding the height information of the carriermechanism back to the control unit 51 as the carrier mechanism movies;an angle information acquirement unit 54 for feeding the rotation angleof the carrier mechanism 40 back to the control unit 51 during therotation process of the carrier mechanism 40.

According to the embodiment of the invention, the height informationacquirement unit 53 and the angle information acquirement unit 54 bothare photoelectrical coded discs, and thus they have the advantage ofanti-interference.

As described above, in the database stored in the memory 61,identification information and physical attributes of various knownliquid articles are stored in a tree structure. FIG. 4 shows a structureused for storing identification information and attribution informationof various liquid articles in the database.

All the samples are divided into several subclasses, such as subclass 1(alcohol), subclass 2 (cola), subclass 3 (milk), . . . , subclass n, andso on. Then, each subclass is subdivided into several subclasses. Forexample, subclass 1 (alcohol) is subdivided into subclass 1.1 (wine),subclass 1.2 (spirit), subclass 1.3 (beer), . . . , subclass 1.n and soon. Each subclass is further subdivided. For example, subclass 1.2(spirit) is subdivided into subclass 1.2.1 (rum), subclass 1.2.2(whisky), subclass 1.2.3 (vodka), . . . , subclass 1.2.n (Chinesespirit). A subclass is subdivided until the difference of the densityand atomic number among respective samples in the subclass is smallerthan a preset value, e.g. the system noise level. Such a subclass is aleaf node in the attribute database structure.

Furthermore, each leaf node is identified with all its father nodes'names, e.g. “40 percent rum of Havana, Cuba”. The identificationcorresponds to reference density and atomic number one by one. In theinspection process, the computer presents the tree structure to the userby levels, and the operator will input the identification information bylevels. For example, the operator wish to acquire physical attribute ofa bottle of 40 percent Havana Ruin from Cuba, he/she can make selectionby levels in the path of alcohol->sprit->rum->rum from Cuba->HavanaRum->40 percent.

The computer makes search as the human operator inputs identificationlevel by level. When the user reaches the last identification, thecorresponding reference density and atomic number are retrieved.

FIG. 5 is a diagram showing the relationship between a DR imaging and aCT imaging. According to the embodiment of the invention, a DR imagingis firstly performed on the liquid article to determine the liquidportion of the liquid article, and then a CT imaging is performed on theliquid portion only so as to improve the inspection speed.

FIG. 6 and FIG. 7 show examples of the result of a DR imaging,respectively. As shown in FIG. 6, after a DR imaging is performed on aliquid article, the liquid in the liquid article can be determined byanalysis of pixels as described below. As shown in FIG. 6, the liquidarticle only contains a kind of liquid. However, as shown in FIG. 7, dueto different attenuation coefficients of different kinds of liquid, whentwo or more kinds of liquid are contained in the liquid article and formseveral layers, the positions of the layer interfaces can be determinedby analysis of pixels of the DR image obtained through a DR imaging.After that, CT imaging can be performed one by one on each layer ofliquid.

FIG. 8 shows an outline flowchart of the liquid article inspectionmethod according to the first embodiment of the invention. As shown inFIG. 8, liquid articles carried by a passenger should pass throughsecurity-inspection, for example, when he/she passes the customs.Firstly at step S110, the human operator places the liquid article to beinspected on the carrier mechanism 40, and acquires the identificationinformation of the liquid article, e.g. 40 percent rum, from the customsdeclaration of the passenger or the remark of the liquid article.

Next, at step S111, the operator input the liquid identification intothe database so that the system will acquire reference density andreference atomic number. Then, the operator presses a start bottom tostart a DR scanning so as to generate a DR image, as shown in FIG. 6 andFIG. 7.

As described above, the purpose of DR scanning is to acquire atransmission image of the inspected liquid articles so that the operatorcan discern the internal structure of the inspected liquid articles tospecify positions in the DR image where CT imaging should be performed.The system software can also use the DR image to automatically identifythe positions of the liquid layers and guide the following CT imaging.The detailed process of the DR imaging will be described below.

What should be noted is that the DR scanning is optional. The CTscanning can be performed by directly specifying several positionswithout guidance of the DR scanning, to improve the inspection speed.For example, it is found that most liquid articles have at least 5 cm ofliquid in height; so 5 cm from the bottom can be used as a pre-specifiedscan position. Furthermore, the operator can visually detect the size ofthe inspected article, and specifies a proper height experientially. Forexample, the scan height of canned Coca Cola can be set as 3 cm, whilethe scan height of a bottle of wine with a thick bottom can be set as 10cm.

Having obtained the DR image, the CT scan positions can be determinedeither by automatic analysis of the DR image (step S113A), or by theoperator using the input device 65 such as a mouse (step S113B), or by amixture of both methods. In such a way, CT scanning is only performed atcertain positions in the liquid articles, so that the inspection isspeeded up without lowering the inspection quality.

Then CT scanning process is performed at step S114 at the determinedpositions in the liquid articles to obtain CT projection data and CTimage are reconstructed based on the CT projection data. Each pixel ofthe CT image denotes the density, atomic number and other physicalattributes of corresponding portion in the liquid articles.

Next, the computer analyzes the CT image by executing an analysisprogram, and obtains the measured density and atomic number at stepS115. Then, at step S116, the measured density and atomic number arecompared with reference density and atomic number retrieved from thedatabase to determine whether they are consistent, such as whether thedifference therebetween is smaller than a predetermined threshold. Atstep S117, the liquid article is indicated to be suspicious if thedifference is larger than the predetermined threshold, and the operatoris alarmed or the inspection result is printed.

Detailed operation of each step will be described with respect to FIGS.9-14. FIG. 9 shows a flowchart of the process of a DR imaging, and FIG.10 shows the arrangement of the DR image data collected by the detectionand collection means 30 during the process of the DR imaging.

As shown in FIG. 9, during the DR imaging, at step S210, a command issent to the controller 50 from the computer 60 to drive the carriermechanism 40 to vertically move along the article passage 20. Thecontroller 50 monitors the height of the carrier mechanism in real timethrough the height information acquirement unit 53 as the carriermechanism vertically moves.

At step S211, the controller 50 sends a trigger signal to the detectionand collection means 30 at intervals of a certain height (for example, 1mm). The detection and collection means 30 receives the trigger signal,and then collects output signals from each detector to obtainhigh-energy detection data and low-energy detection data, and save themin its internal buffer.

At step S212, it is determined whether the carrier mechanism 40 reachesat a specified height or not, such as 500 mm. If not, then the flowproceeds to step S210.

If the carrier mechanism 40 reaches at the specified height, then thecontroller 50 will not send the trigger signal to the detection andcollection means 30. The computer 60 reads collected high and low energydetection data from the detection and collection means 30, and arrangesthem in a matrix to form a DR image. Each pixel of the DR image recordsthe residual intensity of the radiations after transmitting through thearticle, including low-energy radiation intensity and high-energyradiation intensity.

As described above, the CT scan positions are determined based on the DRimage. By either automatic identification or manual specification, a rowid in the DR image is obtained firstly, and then the id is converted tothe height of the carrier mechanism by the computer, and the controller50 is instructed to drive the carrier mechanism 40 to a specifiedposition, and then a CT imaging is performed.

From the flowchart of the DR imaging, each row of the DR imagecorresponds to a height of the carrier mechanism 40. If it is assumedthat the height of the carrier mechanism is 0 when the DR imagingstarts, the carrier mechanism 40 descends during the imaging, andcollection is trigged at intervals of h mm, then the m^(th) row in theDR image corresponds to a height of −m*h of the carrier mechanism.

FIG. 11 shows a flowchart of a process of determining a CT scan positionby processing on the DR image.

In the DR image, the inspected liquid article is generally divided intoa bottle bottom, a liquid portion, a bottle neck, a bottle cover and soon. The liquid portion can be extracted by an image analysis technique,and then the CT scan positions can be determined.

At step S310, a single-value DR image with low noise can be obtained byintegrating and smoothing the high and low energy data of the DR image.For example, the specific method for integrating the high and low energydata can be selection of either the high or low energy data as theintegration result, or weighted combination of the high and low energydata. The smoothing method can be a filtering process of the image witha Gauss filter.

At step S311, the liquid article (foreground) in the smoothed DR imageis extracted, and the air (background) is removed. The specific methodcan set a threshold, and take pixels with values above the threshold asforeground pixels, and other pixels as background pixels. The principleof using a threshold to remove the background is that the liquid articleblocks the radiations, and thus the corresponding pixels in the DR imagehave low values (the DR image records the residual intensity of theradiations).

At step S312, horizontal edge pixels in the smoothed DR image areextracted. The specific method is to calculate the difference betweeneach pixel in the DR image and an adjacent pixel next in verticaldirection, and take the pixel as the horizontal edge pixel if thedifference is larger than a threshold.

At step S313, horizontal edge rows in the smoothed DR image areextracted. The horizontal edge rows are corresponding to the interfacebetween the bottom and the liquid, the interface between the liquid andthe air, and the interface between the cover and the air or interfacesin the container between different liquid layers. The method to get thehorizontal edge rows is to calculate a ratio of the number of thehorizontal edge pixels and the number of foreground pixels on each row,and take the row as the horizontal edge row if the ratio is larger thana threshold (for example, 50%).

At step S314, the DR image is divided vertically, and non-liquid regionsare excluded. Horizontal edge rows in the DR image divide the DR imageinto a number of regions, including a bottle bottom, a liquid portion(may have several layers in different densities), a spacing portioninside the bottle (if any) and a bottle cover. The non-liquid regionscan be excluded by establishing a choosing rule, which can be:

a) In the vertical direction, a region with the number of rows lowerthan a threshold is excluded. The region with a low number of rows is aregion of little thickness, which might be the bottle bottom, the bottlecover or a spacing portion in the top of the bottle (for example, theair at the top of a can). The threshold can be set by investigating thebottle bottom, the bottle cover and the thickness of the air in thecontainer of various containers of liquid packs.

b) In the horizontal direction, a region with average foreground pixelnumber of every row lower than a threshold is excluded. Such a regiongenerally is the slender bottle neck. The threshold can be set byacquiring the width of the bottle necks of various containers of liquidpacking.

At step S315, the CT scan position of the liquid region(s) is determinedto locate respective layers of the liquid, excluding the non-liquidregions. The central rows in the height direction of these regions aretaken as the CT scan positions.

Above described is the process for automatically determining the CT scanpositions. In the case of manually specifying the scan positions, theoperator directly specifies rows on the displayed DR image via the inputdevice 65 as the CT scan positions.

FIG. 12 shows a process of a CT imaging, and FIG. 13 shows thearrangement of the CT projection data during the process of the CTimaging.

As shown in FIG. 12, after the CT positions have been determined, a CTimaging process is performed, i.e. a CT imaging is performed at thedetermined CT scan positions to generate a density-atomic number imageof one slice of the inspected article, to measure the density and atomicnumber of the liquid. As described above, the CT imaging is onlyperformed on the typical positions, and thus the passing time can belargely saved.

At step S410, the computer 60 sends a command to the controller 50 todrive the carrier mechanism 40 to rotate an angle, such as one degree.The controller 50 monitors the angle of the carrier mechanism in realtime via the angle information acquirement unit 54 during the carriermechanism rotates.

At step S411, the monitor 50 sends a trigger signal to the detection andcollection means 30 after a rotation of one degree. The detection andcollection means 30 receives the trigger signal, and collects outputsignals of respective detectors and saves them in its internal buffer.

Next, at step S412, it is determined whether cumulated rotation anglereaches a cycle or not. If not, then the flow proceeds to step S410 andcontinues the above process.

If the cumulated rotation angle reaches a specified angle (such as 360degrees), then at step S413, the rotation ceases, and the controller 50will not send a trigger signal to the detection and collection means 30any more. The computer 60 reads out collected high and low energydetector signals from the detection and collection means 30 and arrangesthem in a data matrix to form CT projection data, as shown in FIG. 13.Each pixel of the CT projection data records the residual intensity ofthe radiations after transmitting through the article, including the lowenergy radiation intensity and the high energy radiation intensity.

At step S414, the computer 60 reconstructs a tomographic image of thedensity and atomic number, i.e. a CT image, from the high and low energyCT projection data by a dual-energy reconstruction algorithm. Each pixelof the CT image records the density and atomic number of the inspectedarticle at the position corresponding to the pixel.

The process of reconstructing tomographic image from the high and low CRprojection data will be described below.

Mathematical Principle of CT

A one-dimensional function p_(θ)(t) can be obtained by linearlyintegrating a two-dimensional distribution u(x,y) along a direction θ,which function is referred to as the projection of u(x,y) at an angle 0.If p_(θ)(t) of respective directions have been obtained, then thetwo-dimensional distribution u(x,y) can be accurately calculated througha Radon transform. The process of calculating a two-dimensionaldistribution from projection is referred to as reconstruction.

In real application, projection of attenuation coefficient of a slice ofan article in respective directions can be measured by an X-ray machineand a detector rotating around the article a cycle. Then thetwo-dimensional distribution of the attenuation coefficient can bereconstructed from the CT principle.

Basis Material Decomposing Model

In the energy range of a mini X-ray security inspection system (<200keV), the attenuation coefficient of radiation can be approximatelyexpressed as following formula (1).

$\begin{matrix}{{\mu (E)} = {{a_{1}{f_{p}(E)}} + {a_{2}{f_{KN}(E)}}}} & (1) \\{a_{1} = {\frac{\rho \; Z}{M}Z^{n}}} & (2) \\{a_{2} = \frac{\rho \; Z}{M}} & (3)\end{matrix}$

In formula (1), the linear attenuation coefficient, μ(E), as a functionof X-ray energy E, is decomposed to f_(p)(E), which demotes thecontribution from photoelectric effect, and f_(KN)(E), the Comptoneffect. Both f_(p)(E) and f_(KN)(E) have known formulas, which areomitted here. The decomposition coefficients a₁ and a₂ are related tothe atomic number, mass number and density, with formulas being shown in(2) and (3), in which Z denotes the atomic number, M denotes the massnumber, ρ denotes the density (g/cm³) and n is a constant.

According to formula (1), with a given X-ray energy distribution, thelinear attenuation coefficient of each substance can be uniquelydetermined by only two coefficients a₁ and a₂. Therefore, if we selecttwo basis materials, such as carbon and aluminum, then and all othermaterials can be expressed as the linear combination of the lineattenuation coefficients of these basis materials, as shown in thefollowing formula (4).

μ(E)=b ₁μ₁(E)+b ₂μ₂(E)  (4)

Formula (4) is just a linear transformation of formula (1), whereinμ₁(E) and μ₂(E) are the linear attenuation coefficients of the selectedbasis materials, and b₁ and b₂ are called basis material coefficients.Another interpretation of formula (4) is that the linear attenuationcoefficient of any material can be regarded as a weighted sum of thelinear attenuation coefficients of two basis materials.

Then we define a characteristic density, ρ*, as the product of the ratioof double atomic number and the mass number with the density, as informula (5).

$\begin{matrix}{\rho^{*} = {\rho \frac{2\; Z}{M}}} & (5)\end{matrix}$

Assume that the atomic numbers and characteristic densities of the twobasis materials are already known as (Z₁, ρ₁*) and (Z₂, ρ₂*)respectively, the atomic number and characteristic density of anymaterial can be derived from the above formulas (1)˜(4) as follows.

$\begin{matrix}{\rho^{*} = {{b_{1}\rho_{1}^{*}} + {b_{2}\rho_{2}^{*}}}} & (6) \\{Z = \left( \frac{{b_{1}\rho_{1}^{*}Z_{1}^{n}} + {b_{2}\rho_{2}^{*}Z_{2}^{n}}}{{b_{1}\rho_{1}^{*}} + {b_{2}\rho_{2}^{*}}} \right)^{1/n}} & (7)\end{matrix}$

Basis Material Projection Model

The energy spectrum generated by an X-ray tube is typically a continuousspectrum. The energy response function of a detector to X-rays is notconstant. Assume that the product of the energy spectrum N(E) and theenergy response function P_(d)(E) is S(E), and S(E) is normalized asfollows,

∫₀ ^(E) ^(m) S(E)dE=1  (8)

then the projection on a projection line can be expressed as followingintegration:

$\begin{matrix}{p = {{{- \ln}\frac{I}{I_{0}}} = {{- \ln}{\int_{0}^{E_{m}}{{S(E)}{\exp \left( {- {\int_{1}{{\mu \left( {E,x,y} \right)}\ {l}}}} \right)}\ {E}}}}}} & (9)\end{matrix}$

in which I₀ and I respectively denote the detector readings before andafter the radiations are attenuated by the article, E_(m) denotes themaximum energy of the radiations, and l denotes the path of theradiations.

The above formula (9) shows the relationship between the measuredprojection p and the two-dimensional distribution μ(x,y). It is obviousthat the formula (9) is not the linear integration of μ(x,y) because theX-ray energy is not a const, and thus does not meet the requirement ofthe mathematical principle of CT.

The conventional reconstruction algorithm neglects such uniformity, as aresult the reconstructed image of μ(x,y) will have an artifact of a cupshape, which is called hardened artifact. If we calculate two sets ofμ(x,y) by conventional reconstruction algorithm, and then deriveinformation such as the atomic number and density, the result will alsohave artifacts.

The present invention solves this problem with basis materialdecomposition model. Substituting formula (4) in formula (9), we willget a basis material projection model,

p=−ln∫₀ ^(E) ^(m) S(E)exp(−∫[μ₁(E)b ₁(x,y)+μ₂(E)b ₂(x,y)]dl)de  (10)

Let

∫₁ b ₁(x,y)dl=B ₁  (11)

∫₁ b ₂(x,y)dl=B ₂  (12)

in which B₁ and B₂ are referred to as the projection of the basismaterial coefficients b₁(x,y) and b₂(x,y). Then the dual-energyprojection data as follows can be obtained by collecting the projectiondata in dual-energy.

p ₁(B ₁ ,B ₂)=−ln∫₀ ^(E) ¹ S ₁(E)exp[−B ₁μ₁(E)−B ₂μ₂(E)]dE  (13)

p ₂(B ₁ ,B ₂)=−ln∫₀ ^(E) ² S ₂(E)exp[−B ₁μ₁(E)−B ₂μ₂(E)]dE  (14)

in which E₁ denotes the maximum energy of the low-energy radiations, andE₂ denotes the maximum energy of the high-energy radiations. After (p₁,p₂) is measured, (B₁, B₂) can be solved based on the formulas (13) and(14), which will be described in the next section. And after (B₁, B₂) inall angles have been obtained, the distribution of the basis materialcoefficients b₁(x,y) and b₂(x,y) can be reconstructed according to theCT reconstruction theory. Then the atomic number and characteristicdensity distribution of the article and the linear attenuationcoefficient of any energy can be calculated according to the basismaterial decomposition model.

Solution of Basis Material Coefficient Projection (B₁, B₂)

Both formulas (13) and (14) are logarithmic integral formulas, which cannot be resolved analytically. The conventional non-linear iterativemethod needs a great deal of calculation, and can not easily obtainstable solutions.

It should be noted that the measured dual-energy projection can beexpressed as follows after the radiations pass through the basismaterials 1 and 2 with thickness of d₁ and d₂:

p ₁=−ln∫₀ ^(E) ¹ S ₁(E)exp[−d ₁μ₁(E)−d ₂μ₂(E)]dE  (15)

p ₂=−ln∫₀ ^(E) ² S ₂(E)exp[−d ₁μ₁(E)−d ₂μ₂(E)]dE  (16)

Comparing formulas (13) and (14) with (15) and (16), it can be seen thatthe measured projection pair (p₁, p₂) is the same. That is, theprojection data pair (B₁, B₂) of the basis materials is just the same asthe thickness pair (d₁, d₂) of the basis materials. Therefore, thecorrespondence between the dual-energy projection data pair (p₁, p₂) andthe basis material coefficient projection data pair (B₁, B₂) can beobtained by measuring the dual-energy projection of different thicknesspair, and a look-up table can be formed. A pair (B₁, B₂) can becalculated from (p₁, p₂) according to the look-up table by linearinterpolation, instead of a complex solution process.

FIG. 14 shows the process for measuring the attributes of the liquid.

As shown in FIG. 14, at step S510, the density image and the atomicnumber image are integrated and smoothed to form a single value CT imagewith low noise. The specific integration method can be selection ofeither the density image or the atomic number image as the integrationresult, or weighted combination of both images. The specific smoothingmethod can be filtering the image with a Gauss filter.

At step S511, the inspected articles (foreground, including the liquidand the pack thereof) in the smoothed CT image is extracted, and the airimage (background) is removed. A specific method is to set a threshold,and take pixels with values above the threshold as foreground pixels,and other pixels as background pixels. The reason is that the densityand atomic number of air are nearly zero, whereas those of the inspectedliquid article are relatively larger.

At step S512, the liquid pixels in the foreground pixels are extracted.A specific method for extraction may include the following steps.Firstly, it establishes a binary image corresponding to the CT image,setting the value of the foreground pixels to one, the value of thebackground pixels to zero. Then the morphological erosion technique isapplied to binary image to remove the packing, since the liquid isalways inside the packing. The times of corrosions can be set inaccordance with the thickness of the packing.

At step S513, the average density and average atomic number of all theliquid pixels in the CT image can be calculated as the output result ofthis measurement.

Furthermore, if the DR image analysis process finds that the liquid hasmultiple layers, the above steps are repeated with respect to each layerto determine if any layer is suspicious. The operator can be informed ofthe final inspection result.

Moreover, if the information of the liquid articles in the database isinsufficient, ie., the system operator cannot find the identificationinformation of a certain article, the database can be expanded. In otherwords, the database can not only be filled by the product manufacturerin the factory, but also be expanded by the operator on site. Forexample, when a new kind of drink appear in the market, the operator cangenerates reference density and reference atomic number from samples ofthe drink. FIG. 15 shows the process of expanding the database.

The basic procedure for adding an item to the database is to measure itsreference density and atomic number, assign a unique identification toit, and then insert it in the identification tree with the referencedensity and atomic number.

As shown in FIG. 15, at step S610, the operator powers on the system,and logs in the database expansion interface. The system enters into theready state after self check. Then the operator places liquid article tobe inspected, which is desired to be added into the database, on thecarrier mechanism 40. At step S611, the computer 60 sends a command tothe controller 50 to trigger the radiation source 10 and the detectionand collection means 30 to perform DR imaging. At step S612A, theposition of the liquid is automatically determined as described above,or at step S612B, the position of the liquid can also be specified bythe operator on the DR image.

Next, at step S615, the operator set identification for the samples ofthe liquid, such as Coca-Cola. At step S616, the identification isassociated with reference density and atomic number and then stored inthe database.

Second Embodiment

The above first embodiment relates to the case that a single liquidarticle is inspected at a time. A process of inspecting a plurality ofliquid articles at a time will be described with respect to FIGS. 16-19.The second embodiment differs from the first embodiment in that thepositions of imaging result displayed on the displayer should correspondto the positions of the articles on the carrier mechanism so that thehuman operator can ascertain which article is suspicious after the CTimage has been obtained. FIG. 16A and FIG. 16B show diagrams of CTimages reconstructed in the case that a plurality of liquid articles areto be inspected according to the second embodiment.

For example, if the operator observes the inspected articles on thecarrier mechanism from the top, then the positions of respectivearticles on the CT images of all layers should correspond to the topview of the carrier mechanism.

FIG. 17A to FIG. 17K show the process how to rotate the CTreconstruction images and/or the carrier mechanism to be aligned withthe position before CT scanning.

FIG. 17A shows a top view of the carrier mechanism 40 when the first CTimaging starts, in which the angle of the carrier mechanism is denotedby an arrow. FIG. 17B shows the first CT image, in which the rotationrange of the carrier mechanism is identified by the dash line. Note thatFIG. 17B is aligned to FIG. 17A by conventional CT reconstructionalgorithm. FIG. 17C shows the first CT image displayed after theinspection, which is the same as FIG. 17B because no further rotation isneeded.

FIG. 17D shows a top view of the carrier mechanism at the n^(th) CTimaging starts. From FIG. 17D it can be seen that the carrier mechanismrotates an angle with respect to that before the first CT imaging. FIG.17E shows the CT image of FIG. 17D and FIG. 17F shows the n^(th) imagedisplayed on the screen after inspection, which is aligned with thefirst CT image by rotation.

FIG. 17G shows a top view of the carrier mechanism at the last CTimaging starts. From FIG. 17G it can be seen that the carrier mechanismrotates an angle with respect to that at the first CT imaging starts.FIG. 17B shows the CT image of FIG. 17G, and FIG. 17I shows the last CTimage displayed on the screen after inspection, which is aligned withthe first layer of the CT image by rotation.

FIG. 17J shows a top view of the carrier mechanism after the last CTimaging ends, in which the carrier mechanism rotates an angle withrespect to that before the first CT imaging starts. FIG. 17K shows a topview of the carrier mechanism after inspection, which returns to theposition of FIG. 17A.

The basic alignment procedure is: after all the CT imaging, the anglesof respective layers of the CT image and the carrier mechanism areadjusted. Firstly, respective layers of the CT images are rotatedaccording to the angles of the carrier mechanism at respective CTimaging starts (the degrees can be obtained by the angle informationacquirement unit 54) so that the positions of the same article in the CTimages of respective layers are aligned, e.g. with the first layer ofCT. Next, the angle of the carrier mechanism is adjusted so that the topview of the carrier mechanism corresponds to the CT image.

For example, assume that N times CT imaging are performed, and the angleof the carrier mechanism is α_(n) at the n^(th) CT imaging starts, andis β_(n) at the n^(th) CT imaging ends. The carrier mechanism rotatescounterclockwise in the top view. In order for the position of thearticle in the n^(th) CT image to be consistent with that in the firstone, the n^(th) CT image rotates by α_(n)−a₁ counterclockwise. Andfinally the carrier mechanism rotates by 360−(β_(N)−α₁) counterclockwiseso as the top view of the carrier mechanism being consistent with the CTimage.

FIG. 18 shows a flowchart for performing inspecting operation in thecase of a plurality of articles are to be inspected. As shown in FIG.18, at step S710, the human operator powers on the system and logs inthe inspection interface. The system enters into the ready state afterself check. Then the operator places the plurality of articles to beinspected, such as article A and article B, on the carrier mechanism 40and presses an inspection button. Here, assume that the article A isplaced at the up right corner of the carrier mechanism, and the articleB is placed at the lower left corner of the carrier mechanism. Besides,the operator inputs respective identification information of article Aand Article B.

At step S711, respective reference density and reference atomic numberare retrieved from the database based on the identification informationof article A and article B. Next, at step S712, the operator presses astart button to perform DR scanning as described above, to generate a DRimage.

After the DR image has been obtained, at step S713A, the DR image isanalyzed to automatically determine the scan position of the CT imaging,or at step S713B, the operator operates the input device 65 such as amouse to specify positions where to perform a CT scanning. In such away, CT scanning is only performed at typical positions in the liquidarticles, whereby the inspection is speeded up without lowering theinspection quality.

Having determining the CT scan positions, a CT scanning process isperformed at step S714, i.e. CT scanning is performed at the determinedpositions in the liquid articles to obtain CT projection data and a CTimage is reconstructed based on the CT projection data. Each pixel ofthe CT image denotes the density and atomic number of correspondingportion in the liquid articles. In the case that the liquid is layered,the CT scanning is repeated for each layer.

After the last CT imaging ends, at step S715 and S716, the carriermechanism and each layer of the CT image are adjusted as above so thatthe positions of respective articles in each layer of the CT image areconsistent (e.g. aligned with those in the CT image of the first layer),and consistent with the real positions of the articles on the carriermechanism (e.g. in the top view), thereby article B and article A can bedistinguished from each other.

At step S717, image partition processing is preformed on the CT imagesof each layer (for example, by using a watershed algorithm) to obtainthe liquid region of each inspected article. At step 718, the averagedensity and average atomic number of respective pixels in each liquidregion are calculated, and they are compared with reference density andatomic number at step S719. At step S720, it is determined whether theinspected article is suspicious.

At step S721, the results of respective layers are gathered and shown tothe operator. One of the gathering methods is to conclude that theresult is “secure” only if all the liquid regions in all the CT imagesare determined to be secure; otherwise the result is “suspicious”.Furthermore, the CT images of respective layers are colorized anddisplayed to the users. The suspicious articles are shown with a certaincolor (such as red), and secure liquid are shown with another color(such as green).

The case in which two liquid articles are inspected is described above.When more liquid articles are to be inspected, a plurality of regions,such as region A, region B, region C and region D shown in FIG. 19, arepartitioned in the surface on which the carrier mechanism carries theliquid articles, as shown in FIG. 19, so that the operator can ascertainthe positions of respective liquid articles. In this way, the operatorcan locate respective liquid articles in corresponding regions, andinput respective liquid identification information for respectiveregions.

Third Embodiment

To improve inspection efficiency, and to help slim articles stand stablyin the barrel, the third embodiment will employ a divided barrel.

The third embodiment differs from the second one in that a dividedbarrel is used in the process of inspecting a plurality of articles. Theoperation of the inspection system according to the third embodimentwill be described with respect to FIGS. 20-25.

FIG. 20 shows a side view of a divided barrel according to an embodimentof the invention, FIG. 21 shows a top view of a divided barrel, and FIG.22 shows a bottom view of a divided barrel.

As shown in FIG. 20, the divided barrel 70 comprises a bottom and a sidewall coupled to the bottom. Protrudes of cone shape or other shape areprovided on the lower surface of the bottom. The three cone-shapedprotrudes can be inserted into the corresponding location holes on thecarrier mechanism 40 so that the divided barrel 70 will rotate as thecarrier mechanism 40 during the rotation of the carrier mechanism 40 toprevent relative motion from occurring therebetween.

Moreover, as shown in FIG. 20, a flange is provided along the top of theside wall to facilitate grasp and portage of the operator. The side wallhas a sharp of a column or a cone, and is made of materials withelasticity, such as Polyethylene (PE) or aluminum.

FIG. 21 is the top view of three kinds of divided barrels. As shown, oneor more dividing parts are provided in the space formed by the bottomand the side wall. The space is divided into plural subspaces to placecorresponding liquid articles. In such a way, if a plurality of liquidarticles is to be inspected at a time, the liquid articles are placed inthe subspaces divided by the dividing parts. In this case, marks can beprovided on the outer surface of the side wall to locate the articles inthe barrel. For example, when one of four articles is determined to besuspicious, the one can be notified to the operator by the correspondingmark of the article on the side wall.

For example, as shown in left of FIG. 21, mark with round sections ofpreset sizes are provided at the end of the dividing parts, or one ofthe dividing parts being shorter than the others is used as the mark forlocating liquid articles.

FIG. 22 is a bottom view of a divided barrel. Though three protrudes areprovided uniformly at the lower surface of the bottom, the protrudes canalso be distributed non-uniformly.

FIG. 23 shows a process how to automatically detect the divided barreland the mark during an inspection operation. As described above, thedivided barrel can be detected by a pattern matching method which istypical in the image processing because the divided barrel has aspecific structure. Taking the first kind of barrel with a crossdividing part as an example, at step S810 a pattern image with a crosscan be established at first, and the center of the pattern is placed onthe center of the CT image to be identified to obtain a matching value.

At step S811, it is determined whether the matching value is larger thana predetermined threshold or not. If not, then the pattern image isrotated until maximum matching of the pattern image and the CT image isobtained. If the matching is larger than a predetermined threshold, thenit is deemed that a divided barrel exists in the CT image; otherwise itis deemed that no divided barrel exists in the CT image.

In the case that a divided barrel exists in the CT image, then at stepS812, the location mark can be detected according to the characteristicsthereof. Again taking the first kind of barrel with a cross dividingpart as an example, the location mark is at top of a dividing line whichis longer than other three dividing lines. After it is determined that adivided barrel exists in the CT image through the pattern matchingmethod, the cross line in the pattern image at maximum matchingsuperposes a dividing line. The location mark can be detected bycomparing the four dividing lines and taking the longest one.

In the case of a multi-layered CT imaging, firstly divided barreldetection and location mark detection are performed on each layer of theCT image. If no divided barrel is detected in respective layers, then itis deemed that no divided barrel is used by the operator. If a dividedbarrel is detected in at least one layer, then it is deemed that adivided barrel is used. If detected location mark positions ofrespective layers are different, then the one with strongest signalintensity can be taken as the final location mark. One method todescribe the signal intensity of the location mark in a layer of the CTimage is to subtract an average value from the maximum value of the fourdividing lines in the layer. The larger the difference is, the strongerthe signal intensity of the location mark is.

FIG. 24A to FIG. 24D shows a diagram of a process of rotating the barrelduring the inspection operation. The divided barrel is adjusted to aspecified position by adjusting the location mark of the barrel to apredetermined position. Taking the first kind of barrel with a crossdividing part as an example, a polar coordinate system is establishedwith the center of the CT image as the origin, positions of each chamberare uniquely determined by the angle coordinates of the location mark.Assume that the angle of the polar coordinate corresponding to thefinally determined location mark in the CT image is γ, and the presetadjustment target of the system is θ, then the adjustment can be done byrotating layers of the CT image and the carrier mechanism by θ−γ, asshown in FIG. 24 below.

As shown in FIGS. 24A and 24B, the divided barrel rotates a certainangle to reach a preset position. Similarly, each layer of the CT imagerotates to be aligned with the rotated divided barrel.

FIG. 25 shows a flowchart of the inspection operation according to athird embodiment of the invention. Steps S910 to S921 are the same assteps S710 to S721 in the above second embodiment. Only steps S922 toS926 will be described.

At step S922, the CT image is analyzed. At step S923, it is determinedwhether there is a divided barrel. In the case of no divided barrel,then the inspection operation ends.

If a barrel is used, then at step S924, the location mark of the barrelis identified determine the positions of each chamber. Next, at stepS925, the carrier mechanism and each layer of the CT image are furtheradjusted so that each chamber of the barrel on the carrier mechanism andeach chamber on each layer of the CT image reach predeterminedpositions.

At step S926, the system lists the results of respective liquid regionsof each layer of the CT image in each chamber, and gathers them todisplay to the user. One gathering method according to the embodiment isto conclude that the result of a chamber is “secure” only if all theliquid regions of all the CT images in this chamber are determined to besecure; otherwise the result of the chamber is “suspicious”.

Fourth Embodiment

The above first to third embodiments describe the case where theinspection method according to the present inventions is used todetermine whether the inspected liquid article is suspicious, but it canbe directly determined whether drugs are concealed in the inspectedliquid article.

The physical attributes (such as density and equivalent atomic number)of the liquid article will change after drugs are concealed therein. Forexample, the density of pure water is 1.00 g/cm³, and the atomic numberthereof is 7.5.

After cocaine of 50 g is resolved in water of 1000 g, the densitychanges to 1.01 g/cm³, and the atomic number becomes 7.6.

The method for calculating the equivalent atomic number of a substance(including mixer) is as follows.

Assume that a substance includes N kinds of elements, and the atomicnumber of respective elements is Z₁, and the percent of the number ofatom's of respective elements is α₁, wherein i=1, 2, . . . , N and

${{\sum\limits_{i = 1}^{N}\alpha_{i}} = 1},$

then the equivalent atomic number of this substance is:

$Z_{eff} = \left\lbrack {\sum\limits_{i = 1}^{N}{\alpha_{i}{Z_{i}^{4.5}/{\sum\limits_{i = 1}^{N}{\alpha_{i}Z_{i}}}}}} \right\rbrack^{\frac{1}{3.5}}$

Therefore, taking water (H₂O) as an example, the calculation of theequivalent atomic number is shown in Table 1 below.

TABLE 1 kind of the atom H O atomic number of 1 8 respective atomspercent of number of 66.7% 33.3% atoms equivalent atomic 7.51 number

After drugs are concealed therein, the change of the atomic number isshown in Table 2 below.

TABLE 2 Without With With With With drugs 5% drugs 10% drugs 15% drugs20% drugs density 1.00 1.01 1.02 1.03 1.04 characteristic 1.11 1.12 1.131.14 1.15 density atomic 7.51 7.62 7.73 7.84 7.95 number

Furthermore, FIG. 26A shows a change curve of the density after drugsare concealed in the liquid, FIG. 26B shows a change curve of the atomicnumber after drugs are concealed in the liquid, and FIG. 26C shows achange curve of the characteristic density after drugs are concealed inthe liquid.

The inspection method according to the embodiment of the presentinvention will be described with respect to FIG. 27.

At step S1010, the operator places a liquid article to be inspected onthe carrier mechanism 40, and acquires the identification information ofthe liquid article, e.g. a bottle of water, from the customs declarationof the passenger or the remark of the liquid article.

Next, at step S1011, the operator retrieves reference density andreference atomic number from the database based on the identificationinformation, such as density of 1.00 (the characteristic density being1.11) g/cm³, and reference atomic number of 7.51. After that, theoperator presses a start button to start DR scanning, to generate a DRimage.

Having obtained the DR image, at step S1013A, the DR image is analyzedto automatically determine CT scan positions, or at step S1013B, CT scanpositions can be specified by the operator operating the input device 65such as a mouse. In such a way, CT scanning is only performed at typicalpositions in the liquid articles, whereby the inspection is speeded upwithout lowering the inspection quality.

Having determining the CT scan positions, a CT scanning process isperformed at step S1014, i.e. a CT scanning is performed at thedetermined positions in the liquid articles to obtain CT projection dataand a CT image is reconstructed based on the CT projection data. Eachpixel of the CT image denotes the density and atomic number ofcorresponding portion in the liquid articles.

Next, the computer analyzes the CT image by executing an analysisprogram, and obtains the measured density and atomic number at stepS1015. For example, the density is 1.02 (characteristic density being1.13) g/cm³, and the atomic number is 7.71. Then, at step S1016,difference of 0.02 g/cm³ between the measured density and referencedensity and difference of 0.20 between the measured atomic number andreference atomic number are acquired. If the drug concealmentdetermination threshold is set as density difference of 0.01 g/cm³ andatomic number of 0.10, then the measured density and atomic numberlocate at the predetermined region. At step S1017, the liquid article isindicated to be suspicious if the difference is larger than thepredetermined threshold, and the operator is alarmed or the inspectionresult is printed.

In order to determine reference density and atomic number, a sample ofthis kind of liquid is measured in advance and the result is stored inthe database. In order to determine the desired threshold of thedifference, it can be manually set to an appropriate value. If it iswished to detect minim drug, then the threshold can be set as a relativesmaller value. The risk of doing so is misdetection which will occur toan inspected article without drugs due to system noise. On the contrary,if it is wished to reduce misdetection for articles without drugs, thethreshold should be set as a larger value. The risk of doing so isnon-detection which will occur to articles with minim drugs but thedensity difference being lower than the determination threshold.

As known to those skilled in the art, though the case where a singlearticle is to be inspected is described above, the above fourthembodiment is also applicable in the case of multiple article inspectionas the second embodiment and the third embodiment are.

[First Variation]

Though the present invention is described with respect to the case offirst DR imaging and then CT imaging, spiral CT imaging also can beadopted to inspect liquid articles according to the present invention.

A set of spiral CT images can be obtained by performing CT on liquidarticle. The position of the liquid in the liquid article can bedetermined by comparing and analyzing pixels in the set of CT images,and whether the liquid is layered can also be determined. The physicalattributes, such as density and atomic number, of the liquid ofrespective positions can be obtained in a similar manner as describedabove. For example, when spiral CT imaging is performed on the liquidarticle shown in FIG. 28, and the spiral pitch is 2 cm, then a set of CTimages as shown in FIGS. 29A-29M can be obtained. In this way, theposition of the liquid in the liquid article can be obtained byanalyzing pixels in the spiral CT images. Here, the spiral CT imagingcan be high pitch CT imaging or normal pitch CT imaging.

Moreover, though the above description takes the density and atomicnumber as examples, the present invention is also effective when onlyone attribute, either the density or atomic number, is used, or evenmore physical attributes are used to identify suspicious articles.

[Second Variation]

Though in the above description first the DR imaging and thendual-energy CT imaging are performed to acquire the density and atomicnumber of the liquid, the DR imaging is optional. Predeterminedpositions where to perform dual-energy CT imaging can be specified inadvance for various liquid articles to acquire the density and atomicnumber of the liquid.

While exemplary embodiments of the present invention have been describedhereinabove, it should be clear to those skilled in the art that anyvariations and/or modifications of the basic inventive concepts willstill fall within the scope of the present invention, as defined in theappended claims.

1-41. (canceled)
 42. A method of inspecting a liquid article comprising:performing a DR imaging on the liquid article to generate a transmissionimage; determining from the transmission image at least one rows in theheight direction of a liquid portion in the liquid article at which CTscan is to be performed; performing dual-energy CT scan at thedetermined rows to generate CT image data; determining a density andatomic number from the generated CT image data; comparing the densityand atomic number determined from the CT image data with the respectivereference density and atomic number preset in a database; and outputtinginformation indicative of that the liquid article conceals drug if thecomparison results satisfy a predetermined condition.
 43. The method ofclaim 42, wherein the step of determining at least one rows comprises:analyzing the transmission image using the image processing technique toobtain the information about the liquid portion in the liquid article asanalysis results; and determining the at least one rows based on theanalysis results.
 44. The method of claim 43, wherein the informationabout the liquid portion comprises location information of liquidportions in the liquid article, and at least one rows are determinedbased on the location information of liquid portions in the liquidarticle.
 45. The method of claim 42, wherein the step of determining atleast one rows comprises: displaying the transmission image; andreceiving the at least one rows set with respect to the transmissionimage using an input device.
 46. The method of claim 42, wherein thestep of performing dual-energy CT scan comprises: performing adual-energy CT scan on the liquid article to generate a high-energy CTimage data and a low-energy CT image data; and taking one of thehigh-energy CT image data, low-energy CT image data and the combinationof the high-energy CT image data and the low-energy CT image data as theCT image data.
 47. The method of claim 42, wherein the step ofoutputting comprises: outputting the information indicative of that theliquid article conceals drug in the case that the physical attributevalues and the reference values have a difference lower than apredetermined threshold value.
 48. An apparatus of inspecting a liquidarticle comprising: a radiation source adapted to emit radiation beams;a detection and acquisition device adapted to detect and acquireradiation signals transmitted through the liquid article; a controlleradapted to control the detection and acquisition device to perform DRimaging on the liquid article to generate a transmission image, andperform CT imaging on the liquid article at least one rows in the heightdirection of a liquid portion in the liquid article to generate CT imagedata; a computer adapted to determine a density and atomic number fromthe generated CT image data, compare in the density and atomic numberdetermined from the CT image data with respective reference density andatomic number preset in a database, and output information indicative ofthat the liquid article conceals drug if the comparison results satisfya predetermined condition, wherein the computer is further adapted tosend to the controller a signal to indicate the at least one rows atwhich the CT scan is performed.
 49. The apparatus of claim 48, whereinthe computer is further adapted to analyze the transmission image usingan image processing technique to obtain information about liquidportions in the liquid article as analysis results, and determine therows based on the analysis results.
 50. The apparatus of claim 49,wherein the information about the liquid portion comprises locationinformation of liquid portions in the liquid article, and the computeris further adapted to determine the at least one rows based on thelocation information of the liquid portions in the liquid article. 51.The apparatus of claim 48, wherein the computer comprises: a displaydevice that displays the transmission image; an input device thatreceives the rows set with respect to the transmission image at whichthe CT scan is to be performed.
 52. The apparatus of claim 48, whereinthe controller is further adapted to control the radiation source andthe detection and acquisition device to perform a dual-energy CT scan onthe liquid article to generate a high-energy CT image data and alow-energy CT image data; and the computer is further adapted to takeone of the high-energy CT image data, low-energy CT image data and thecombination of the high-energy CT image data and the low-energy CT imagedata as the CT image data.
 53. The apparatus of claim 48, wherein thecomputer is further adapted to output the information indicative of thatthe liquid article conceals drug in the case that the physical attributevalues and the reference values have a difference lower than apredetermined threshold value.
 54. A method of inspecting a liquidarticle, comprising: retrieving from a database at least one rows of aliquid portion using information on the external surface of the liquidarticle; placing the liquid article on a carrying stage; determiningrows at which CT scan are to be performed based on the rows; performingCT scan on the liquid article at the rows to obtain CT image data; andanalyzing the CT image data to determine whether the liquid articleconceals drug.
 55. The method of claim 54, wherein the information onthe external surface of the liquid article comprises at least one oftypes of product, producer and size.
 56. The method of claim 54, whereinthe step of performing CT scan comprising: performing a dual-energy CTscan on the liquid article to generate a high-energy CT image data and alow-energy CT image data; and taking one of the high-energy CT imagedata, low-energy CT image data and the combination of the high-energy CTimage data and the low-energy CT image data as the CT image data. 57.The method of claim 54, wherein the step of analyzing comprises:analyzing the CT image data to obtain the physical attribute valuesabout the liquid article, wherein the physical attribute valuescomprises at least one of atomic number and density; and determiningwhether the at least one liquid article conceals drug by comparing atleast one physical attribute values contained in the CT image data withrespective reference physical attribute values preset in a database.